Ultrasonic sensing device

ABSTRACT

An electronic device comprises a CMOS substrate having a first surface and a second surface opposite the first surface. A plurality of ultrasonic transducers is provided having a transmit/receive surface. A contact surface is piezoelectrically associated with the plurality of ultrasonic transducers and is formed on the first surface of the CMOS substrate. The plurality of ultrasonic transducers is disposed on the second surface of the CMOS substrate, with the transmit/receive side attached to the second surface thereof such that the CMOS substrate is between the plurality of ultrasonic transducers and the platen. An image sensing system is also provided, together with a method for ultrasonic sensing in the electronic device.

RELATED APPLICATIONS

This application claims priority to and is a continuation of theco-pending patent application having application Ser. No. 15/670,976,entitled “AN ULTRASONIC SENSING DEVICE,” with filing date Aug. 7, 2017,by Berger, et al., and assigned to the assignee of the presentinvention, the disclosure of which is hereby incorporated herein byreference in its entirety.

BACKGROUND

Piezoelectric materials facilitate conversion between mechanical energyand electrical energy. Moreover, a piezoelectric material can generatean electrical signal when subjected to mechanical stress, and canvibrate when subjected to an electrical voltage. Piezoelectric materialsare widely utilized in piezoelectric ultrasonic transducers to generateacoustic waves based on an actuation voltage applied to electrodes ofthe piezoelectric ultrasonic transducer.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthe Description of Embodiments, illustrate various embodiments of thesubject matter and, together with the Description of Embodiments, serveto explain principles of the subject matter discussed below. Unlessspecifically noted, the drawings referred to in this Brief Descriptionof Drawings should be understood as not being drawn to scale. Herein,like items are labeled with like item numbers.

FIG. 1A is a diagram illustrating a piezoelectric micromachinedultrasonic transducer (PMUT) device having a center pinned membrane,according to some embodiments.

FIG. 1B is a diagram illustrating a PMUT device having an unpinnedmembrane, according to some embodiments.

FIG. 2 is a diagram illustrating an example of membrane movement duringactivation of a PMUT device having a center pinned membrane, accordingto some embodiments.

FIG. 3 is a diagram illustrating a configuration of an electronic devicehaving an inverted design, according to some embodiments.

FIG. 4 is a diagram illustrating an ultrasonic transducer used in anultrasonic fingerprint sensing system, according to some embodiments.

FIG. 5 is a diagram illustrating in cross-section one embodiment of anintegrated sensor of the present teachings formed by wafer bonding.

FIG. 6 is a diagram illustrating an alternate embodiment of FIG. 3, inwhich the electrodes are repositioned in order to increase signalstrength, according to some embodiments.

FIG. 7 is a diagram illustrating an alternate embodiment, similar toFIG. 6, in which the ultrasonic membrane is reconfigured to maximizedisplacement of structures, according to some embodiments.

FIG. 8 is a diagram illustrating an alternate embodiment of FIG. 3, inwhich the PMUT configuration is replaced with a lead zirconate titanate(PZT) structure, according to some embodiments.

FIG. 9 is a diagram illustrating an embodiment, similar to FIG. 8, inwhich the shape of the PZT structure is changed, according to someembodiments.

FIG. 10 is a diagram illustrating an alternate embodiment of FIG. 3,employing a hybrid PMUT-PZT structure, according to some embodiments.

FIG. 11 is a top plan view that illustrates a single transmissionstructure surrounded by an array of drive structures for increasedacoustic injection, according to some embodiments

FIG. 12 is a flow chart illustrating one embodiment of a method forultrasonic sensing in an electronic device.

FIG. 13 is a block diagram of an example mobile electronic device uponwhich embodiments described herein may be implemented.

DESCRIPTION OF EMBODIMENTS

The following Description of Embodiments is merely provided by way ofexample and not of limitation. Furthermore, there is no intention to bebound by any expressed or implied theory presented in the precedingbackground or in the following Description of Embodiments.

Reference will now be made in detail to various embodiments of thesubject matter, examples of which are illustrated in the accompanyingdrawings. While various embodiments are discussed herein, it will beunderstood that they are not intended to limit to these embodiments. Onthe contrary, the presented embodiments are intended to coveralternatives, modifications and equivalents, which may be includedwithin the spirit and scope the various embodiments as defined by theappended claims. Furthermore, in this Description of Embodiments,numerous specific details are set forth in order to provide a thoroughunderstanding of embodiments of the present subject matter. However,embodiments may be practiced without these specific details. In otherinstances, well known methods, procedures, components, and circuits havenot been described in detail as not to unnecessarily obscure aspects ofthe described embodiments.

Notation and Nomenclature

Some portions of the detailed descriptions which follow are presented interms of procedures, logic blocks, processing and other symbolicrepresentations of operations on data within an electrical device. Thesedescriptions and representations are the means used by those skilled inthe data processing arts to most effectively convey the substance oftheir work to others skilled in the art. In the present application, aprocedure, logic block, process, or the like, is conceived to be one ormore self-consistent procedures or instructions leading to a desiredresult. The procedures are those requiring physical manipulations ofphysical quantities. Usually, although not necessarily, these quantitiestake the form of acoustic (e.g., ultrasonic) signals capable of beingtransmitted and received by an electronic device and/or electrical ormagnetic signals capable of being stored, transferred, combined,compared, and otherwise manipulated in an electrical device.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise as apparent from the followingdiscussions, it is appreciated that throughout the description ofembodiments, discussions utilizing terms such as “transmitting,”“receiving,” “sensing,” “generating,” “imaging,” or the like, refer tothe actions and processes of an electronic device such as an electricaldevice.

Embodiments described herein may be discussed in the general context ofprocessor-executable instructions residing on some form ofnon-transitory processor-readable medium, such as program modules,executed by one or more computers or other devices. Generally, programmodules include routines, programs, objects, components, datastructures, etc., that perform particular tasks or implement particularabstract data types. The functionality of the program modules may becombined or distributed as desired in various embodiments.

In the figures, a single block may be described as performing a functionor functions; however, in actual practice, the function or functionsperformed by that block may be performed in a single component or acrossmultiple components, and/or may be performed using hardware, usingsoftware, or using a combination of hardware and software. To clearlyillustrate this interchangeability of hardware and software, variousillustrative components, blocks, modules, logic, circuits, and stepshave been described generally in terms of their functionality. Whethersuch functionality is implemented as hardware or software depends uponthe particular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure. Also, the example systems describedherein may include components other than those shown, includingwell-known components.

Various techniques described herein may be implemented in hardware,software, firmware, or any combination thereof, unless specificallydescribed as being implemented in a specific manner. Any featuresdescribed as modules or components may also be implemented together inan integrated logic device or separately as discrete but interoperablelogic devices. If implemented in software, the techniques may berealized at least in part by a non-transitory processor-readable storagemedium comprising instructions that, when executed, perform one or moreof the methods described herein. The non-transitory processor-readabledata storage medium may form part of a computer program product, whichmay include packaging materials.

The non-transitory processor-readable storage medium may comprise randomaccess memory (RAM) such as synchronous dynamic random access memory(SDRAM), read only memory (ROM), non-volatile random access memory(NVRAM), electrically erasable programmable read-only memory (EEPROM),FLASH memory, other known storage media, and the like. The techniquesadditionally, or alternatively, may be realized at least in part by aprocessor-readable communication medium that carries or communicatescode in the form of instructions or data structures and that can beaccessed, read, and/or executed by a computer or other processor.

Various embodiments described herein may be executed by one or moreprocessors, such as one or more motion processing units (MPUs), sensorprocessing units (SPUs), host processor(s) or core(s) thereof, digitalsignal processors (DSPs), general purpose microprocessors, applicationspecific integrated circuits (ASICs), application specific instructionset processors (ASIPs), field programmable gate arrays (FPGAs), aprogrammable logic controller (PLC), a complex programmable logic device(CPLD), a discrete gate or transistor logic, discrete hardwarecomponents, or any combination thereof designed to perform the functionsdescribed herein, or other equivalent integrated or discrete logiccircuitry. The term “processor,” as used herein may refer to any of theforegoing structures or any other structure suitable for implementationof the techniques described herein. As is employed in the subjectspecification, the term “processor” can refer to substantially anycomputing processing unit or device comprising, but not limited tocomprising, single-core processors; single-processors with softwaremultithread execution capability; multi-core processors; multi-coreprocessors with software multithread execution capability; multi-coreprocessors with hardware multithread technology; parallel platforms; andparallel platforms with distributed shared memory. Moreover, processorscan exploit nano-scale architectures such as, but not limited to,molecular and quantum-dot based transistors, switches and gates, inorder to optimize space usage or enhance performance of user equipment.A processor may also be implemented as a combination of computingprocessing units.

In addition, in some aspects, the functionality described herein may beprovided within dedicated software modules or hardware modulesconfigured as described herein. Also, the techniques could be fullyimplemented in one or more circuits or logic elements. A general purposeprocessor may be a microprocessor, but in the alternative, the processormay be any conventional processor, controller, microcontroller, or statemachine. A processor may also be implemented as a combination ofcomputing devices, e.g., a combination of an SPU/MPU and amicroprocessor, a plurality of microprocessors, one or moremicroprocessors in conjunction with an SPU core, MPU core, or any othersuch configuration.

Overview of Discussion

Discussion begins with a description of an example PiezoelectricMicromachined Ultrasonic Transducer (PMUT), in accordance with variousembodiments. Example arrays including PMUT devices are then described.Example operations of the example arrays of PMUT devices are thenfurther described.

A conventional piezoelectric ultrasonic transducer able to generate anddetect pressure waves can include a membrane with the piezoelectricmaterial, a supporting layer, and electrodes combined with a cavitybeneath the electrodes. Miniaturized versions are referred to as PMUTs.Typical PMUTs use an edge anchored membrane or diaphragm that maximallyoscillates at or near the center of the membrane at a resonant frequency(f) proportional to h/a², where h is the thickness, and a is the radiusof the membrane. Higher frequency membrane oscillations can be createdby increasing the membrane thickness, decreasing the membrane radius, orboth. Increasing the membrane thickness has its limits, as the increasedthickness limits the displacement of the membrane. Reducing the PMUTmembrane radius also has limits, because a larger percentage of PMUTmembrane area is used for edge anchoring.

Embodiments describes herein relate to a PMUT device for ultrasonic wavegeneration and sensing. In accordance with various embodiments, an arrayof such PMUT devices is described. The PMUT includes a substrate and anedge support structure connected to the substrate. A membrane isconnected to the edge support structure such that a cavity is definedbetween the membrane and the substrate, where the membrane is configuredto allow movement at ultrasonic frequencies. The membrane includes apiezoelectric layer and first and second electrodes coupled to opposingsides of the piezoelectric layer. An interior support structure isdisposed within the cavity and connected to the substrate and themembrane.

The described PMUT device and array of PMUT devices can be used forgeneration of acoustic signals or measurement of acoustically senseddata in various applications, such as, but not limited to, medicalapplications, security systems, biometric systems (e.g., fingerprintsensors and/or motion/gesture recognition sensors), mobile communicationsystems, industrial automation systems, consumer electronic devices,robotics, etc. In one embodiment, the PMUT device can facilitateultrasonic signal generation and sensing (transducer). Moreover,embodiments describe herein provide a sensing component including asilicon wafer having a two-dimensional (or one-dimensional) array ofultrasonic transducers.

Embodiments described herein provide a PMUT that operates at a highfrequency for reduced acoustic diffraction through high acousticvelocity materials (e.g., glass, metal), and for shorter pulses so thatspurious reflections can be time-gated out. Embodiments described hereinalso provide a PMUT that has a low quality factor providing a shorterring-up and ring-down time to allow better rejection of spuriousreflections by time-gating. Embodiments described herein also provide aPMUT that has a high fill-factor providing for large transmit andreceive signals.

Piezoelectric Micromachined Ultrasonic Transducer (PMUT)

Systems and methods disclosed herein, in one or more aspects provideefficient structures for an acoustic transducer (e.g., a piezoelectricactuated transducer or PMUT). One or more embodiments are now describedwith reference to the drawings, wherein like reference numerals are usedto refer to like elements throughout. In the following description, forpurposes of explanation, numerous specific details are set forth inorder to provide a thorough understanding of the various embodiments. Itmay be evident, however, that the various embodiments can be practicedwithout these specific details. In other instances, well-knownstructures and devices are shown in block diagram form in order tofacilitate describing the embodiments in additional detail.

As used in this application, the term “or” is intended to mean aninclusive “or” rather than an exclusive “or”. That is, unless specifiedotherwise, or clear from context, “X employs A or B” is intended to meanany of the natural inclusive permutations. That is, if X employs A; Xemploys B; or X employs both A and B, then “X employs A or B” issatisfied under any of the foregoing instances. In addition, thearticles “a” and “an” as used in this application and the appendedclaims should generally be construed to mean “one or more” unlessspecified otherwise or clear from context to be directed to a singularform. In addition, the word “coupled” is used herein to mean direct orindirect electrical or mechanical coupling. In addition, the word“example” is used herein to mean serving as an example, instance, orillustration.

FIG. 1A is a diagram illustrating a PMUT device 100 having a centerpinned membrane, according to some embodiments. PMUT device 100 includesan interior pinned membrane 120 positioned over a substrate 140 todefine a cavity 130. In one embodiment, membrane 120 is attached both toa surrounding edge support 102 and interior support 104. In oneembodiment, edge support 102 is connected to an electric potential. Edgesupport 102 and interior support 104 may be made of electricallyconducting materials, such as and without limitation, aluminum,molybdenum, or titanium. Edge support 102 and interior support 104 mayalso be made of dielectric materials, such as silicon dioxide, siliconnitride or aluminum oxide that have electrical connections the sides orin vias through edge support 102 or interior support 104, electricallycoupling first electrode 106 to electrical wiring in substrate 140.

In one embodiment, both edge support 102 and interior support 104 areattached to a substrate 140. In various embodiments, substrate 140 mayinclude at least one of, and without limitation, silicon or siliconnitride. It should be appreciated that substrate 140 may includeelectrical wirings and connection, such as aluminum or copper. In oneembodiment, substrate 140 includes a CMOS logic wafer bonded to edgesupport 102 and interior support 104. In one embodiment, the membrane120 comprises multiple layers. In an example embodiment, the membrane120 includes first electrode 106, piezoelectric layer 110, and secondelectrode 108, where first electrode 106 and second electrode 108 arecoupled to opposing sides of piezoelectric layer 110. As shown, firstelectrode 106 is coupled to a lower surface of piezoelectric layer 110and second electrode 108 is coupled to an upper surface of piezoelectriclayer 110. It should be appreciated that, in various embodiments, PMUTdevice 100 is a microelectromechanical (MEMS) device.

In one embodiment, membrane 120 also includes a mechanical support layer112 (e.g., stiffening layer) to mechanically stiffen the layers. Invarious embodiments, mechanical support layer 112 may include at leastone of, and without limitation, silicon, silicon oxide, silicon nitride,aluminum, molybdenum, titanium, etc. In one embodiment, PMUT device 100also includes an acoustic coupling layer 114 above membrane 120 forsupporting transmission of acoustic signals. It should be appreciatedthat acoustic coupling layer can include air, liquid, gel-likematerials, or other materials for supporting transmission of acousticsignals. In one embodiment, PMUT device 100 also includes platen layer116 above acoustic coupling layer 114 for containing acoustic couplinglayer 114 and providing a contact surface for a finger or other sensedobject with PMUT device 100. It should be appreciated that, in variousembodiments, acoustic coupling layer 114 provides a contact surface,such that platen layer 116 is optional. Moreover, it should beappreciated that acoustic coupling layer 114 and/or platen layer 116 maybe included with or used in conjunction with multiple PMUT devices. Forexample, an array of PMUT devices may be coupled with a single acousticcoupling layer 114 and/or platen layer 116.

FIG. 1B is identical to FIG. 1A in every way, except that the PMUTdevice 100′ of FIG. 1B omits the interior support 104 and thus membrane120 is not pinned (e.g., is “unpinned”). There may be instances in whichan unpinned membrane 120 is desired. However, in other instances, apinned membrane 120 may be employed.

FIG. 2 is a diagram illustrating an example of membrane movement duringactivation of pinned PMUT device 100, according to some embodiments. Asillustrated with respect to FIG. 2, in operation, responsive to anobject proximate the platen layer 116, the electrodes 106 and 108deliver a high frequency electric charge to the piezoelectric layer 110,causing those portions of the membrane 120 not pinned to the surroundingedge support 102 or interior support 104 to be displaced upward into theacoustic coupling layer 114. This generates a pressure wave that can beused for signal probing of the object. Return echoes can be detected aspressure waves causing movement of the membrane, with compression of thepiezoelectric material in the membrane causing an electrical signalproportional to amplitude of the pressure wave.

The described PMUT device 100 can be used with almost any electricaldevice that converts a pressure wave into mechanical vibrations and/orelectrical signals. In one aspect, the PMUT device 100 can comprise anacoustic sensing element (e.g., a piezoelectric element) that generatesand senses ultrasonic sound waves. An object in a path of the generatedsound waves can create a disturbance (e.g., changes in frequency orphase, reflection signal, echoes, etc.) that can then be sensed. Theinterference can be analyzed to determine physical parameters such as(but not limited to) distance, density and/or speed of the object. As anexample, the PMUT device 100 can be utilized in various applications,such as, but not limited to, fingerprint or physiologic sensors suitablefor wireless devices, industrial systems, automotive systems, robotics,telecommunications, security, medical devices, etc. For example, thePMUT device 100 can be part of a sensor array comprising a plurality ofultrasonic transducers deposited on a wafer, along with various logic,control, and communication electronics. A sensor array may comprisehomogenous or identical PMUT devices 100, or a number of different orheterogonous device structures.

In various embodiments, the PMUT device 100 employs a piezoelectriclayer 110, comprised of materials such as, but not limited to, aluminumnitride (AlN), lead zirconate titanate (PZT), scandium doped aluminumnitride (ScAlN), quartz, polyvinylidene fluoride (PVDF), and/or zincoxide, to facilitate both acoustic signal production and sensing. Thepiezoelectric layer 110 can generate electric charges under mechanicalstress and conversely experience a mechanical strain in the presence ofan electric field. For example, the piezoelectric layer 110 can sensemechanical vibrations caused by an ultrasonic signal and produce anelectrical charge at the frequency (e.g., ultrasonic frequency) of thevibrations. Additionally, the piezoelectric layer 110 can generate anultrasonic wave by vibrating in an oscillatory fashion that might be atthe same frequency (e.g., ultrasonic frequency) as an input currentgenerated by an alternating current (AC) voltage applied across thepiezoelectric layer 110. It should be appreciated that the piezoelectriclayer 110 can include almost any material (or combination of materials)that exhibits piezoelectric properties, such that the structure of thematerial does not have a center of symmetry and a tensile or compressivestress applied to the material alters the separation between positiveand negative charge sites in a cell causing a polarization at thesurface of the material. The polarization is directly proportional tothe applied stress and is direction dependent so that compressive andtensile stresses results in electric fields of opposite polarizations.

Further, the PMUT device 100 comprises electrodes 106 and 108 thatsupply and/or collect the electrical charge to/from the piezoelectriclayer 110. It should be appreciated that electrodes 106 and 108 can becontinuous and/or patterned electrodes (e.g., in a continuous layerand/or a patterned layer). For example, as illustrated, the firstelectrode 106 is a patterned electrode and the second electrode 108 is acontinuous electrode. As an example, electrodes 106 and 108 can becomprised of almost any metal layers or other conducting material, suchas, but not limited to, aluminum (Al), titanium (Ti), molybdenum (Mo),etc., which are coupled with an on opposing sides of the piezoelectriclayer 110. In one embodiment, PMUT device also includes a thirdelectrode (not shown).

According to an embodiment, the acoustic impedance of acoustic couplinglayer 114 is selected to be similar to the acoustic impedance of theplaten layer 116, such that the acoustic wave is efficiently propagatedto/from the membrane 120 through acoustic coupling layer 114 and platenlayer 116. As an example, the platen layer 116 can comprise variousmaterials having an acoustic impedance in the range between 0.8 to 4Mega Rayleigh (MRayl), such as, but not limited to, plastic, resin,rubber, Teflon, epoxy, etc. In another example, the platen layer 116 cancomprise various materials having a high acoustic impedance (e.g., anacoustic impendence greater than 10 MRayl), such as, but not limited to,glass, aluminum-based alloys, sapphire, etc. Typically, the platen layer116 can be selected based on an application of the sensor. For instance,in fingerprinting applications, platen layer 116 can have an acousticimpedance that matches (e.g., exactly or approximately) the acousticimpedance of human skin (e.g., 1.6×10⁶ Rayl). Further, in one aspect,the platen layer 116 can further include a thin layer of anti-scratchmaterial. In various embodiments, the anti-scratch layer of the platenlayer 116 is less than the wavelength of the acoustic wave that is to begenerated and/or sensed to provide minimum interference duringpropagation of the acoustic wave. As an example, the anti-scratch layercan comprise various hard and scratch-resistant materials (e.g., havinga Mohs hardness of over 7 on the Mohs scale), such as, but not limitedto sapphire, glass, titanium nitride (TiN), silicon carbide (SiC),diamond, etc. As an example, PMUT device 100 can operate at 20 MHz andaccordingly, the wavelength of the acoustic wave propagating through theacoustic coupling layer 114 and platen layer 116 can be 70-150 microns.In this example scenario, insertion loss can be reduced and acousticwave propagation efficiency can be improved by utilizing an anti-scratchlayer having a thickness of 1 micron and the platen layer 116 as a wholehaving a thickness of 1-2 millimeters. It is noted that the term“anti-scratch material” as used herein relates to a material that isresistant to scratches and/or scratch-proof and provides substantialprotection against scratch marks.

In accordance with various embodiments, the PMUT device 100 can includemetal layers (e.g., aluminum (Al), titanium (Ti), molybdenum (Mo), etc.)patterned to form first electrode 106 in particular shapes (e.g., ring,circle, square, octagon, hexagon, etc.) that are defined in-plane withthe membrane 120. Electrodes can be placed at a maximum strain area ofthe membrane 120 or placed at close to either or both the surroundingedge support 102 and interior support 104. Furthermore, in one example,the second electrode 108 can be formed as a continuous layer providing aground plane in contact with mechanical support layer 112, which can beformed from silicon or other suitable mechanical stiffening material. Instill other embodiments, the first electrode 106 can be routed along theinterior support 104, advantageously reducing parasitic capacitance ascompared to routing along the edge support 102.

For example, when actuation voltage is applied to the electrodes, themembrane 120 will deform and move out of plane. The motion then pushesthe acoustic coupling layer 114 it is in contact with and an acoustic(ultrasonic) wave is generated. Oftentimes, vacuum is present inside thecavity 130 and therefore damping contributed from the media within thecavity 130 can be ignored. However, the acoustic coupling layer 114 onthe other side of the membrane 120 can substantially change the dampingof the PMUT device 100. For example, a quality factor greater than 20can be observed when the PMUT device 100 is operating in air withatmosphere pressure (e.g., acoustic coupling layer 114 is air) and candecrease lower than 2 if the PMUT device 100 is operating in water(e.g., acoustic coupling layer 114 is water).

A potential issue with the above-described design is that the soundwaves travel through the epoxy, which has a low acoustic impedance andis not well matched with hard cover materials such as glass or metal.Also, reflection from the backside of the CMOS can also give unwantedreflections. This means that the epoxy thickness and properties have tobe controlled very well, and changing thickness is costly in terms offabrication molds and other features.

The PMUT device 100 as discussed in FIGS. 1A-1B and 2 is designed totransmit the acoustic waves to platen 116, and may be used to imageobjects in contact with platen 116. As such, PMUT device 100 detects theacoustic waves that are reflected from the object in contact with platen116. In addition to the acoustic waves transmitted to the platen and theobject, acoustic waves are also transmitted into substrate 140, forexample, through edge support 102 and interior support 104 which are incontact with substrate 140. Any acoustic waves that enter the substratemay get reflected at any boundary with a change in acoustic impedance.Therefore, many acoustic waves could reflect from the backside of thesubstrate, and may finally be detected by the PMUT structure. Thus, theacoustic waves from the substrate and the acoustic waves from the objecton the platen may both be detected at the same time. This means that anyimage of the object and the ‘image’ of the back side of substrate willbe superimposed and this negatively influence the image quality of theobject on the platen. The CMOS substrate itself is made up of different(metal) layers, but because the acoustic impendences of these layers arenearly identical, only minor acoustic reflection takes place.

In order to overcome the above-mentioned problems, and in accordancewith the teachings herein, an electronic device is provided with aninverted design compared with the design depicted in FIGS. 1A-1B and 2.The electronic device with the inverted layout comprises a CMOSsubstrate having a first surface and a second surface opposite the firstsurface. A plurality of ultrasonic transducers is provided, having atransmit/receive surface. A platen having a contact surface ispiezoelectrically associated with the plurality of ultrasonictransducers and is formed on the first surface of the CMOS substrate.The term “piezoelectrically associated with” refers to a piezoelectricdevice that uses the piezoelectric effect to measure changes inpressure, acceleration, temperature, strain, or force by converting themto an electrical charge. In the context as used herein, any object incontact with the contact surface of the platen may be imaged because thereflected acoustic waves are converted to an electrical charge by theultrasonic transducers that are piezoelectrically associated with theplaten.

The plurality of ultrasonic transducers is disposed on the secondsurface of the CMOS substrate, with the transmit/receive surfaceattached to the second surface thereof such that the CMOS substrate isbetween the plurality of ultrasonic transducers and the platen.

FIG. 3 shows an example of the inverted design, in which the PMUT (orother ultrasonic transducer) transmits ultrasonic signals through theCMOS. All the different layers and component are substantially identicalto FIG. 1A. Although the interior support 104 is shown in FIG. 3, itcould be omitted, as in FIG. 1B The main differences between FIGS. 1Band 3 lie in the acoustic coupling layers 114 and the acousticabsorption layer 118. The main purpose of acoustic coupling layer 114 inFIG. 3 is to provide contact and adhesion of platen 116 to CMOSsubstrate 140. If the platen 116 and the CMOS substrate 140 are bothhard materials, then small airgaps may occur when both are mountedtogether, and these air gaps may prevent the transfer of the acousticwaves into the platen 116. If the platen 116 makes perfect contact withthe CMOS substrate 140, then no acoustic coupling layer 114 may beneeded. This may be the case if the platen 116 is applied in an(initial) liquid- or gel-like form. In some embodiments, the backside140 a of substrate 140 may be used as the contact surface, and noadditional platen 116 is required.

Acoustic absorption layer 118 may be applied to the back 120 a ofmembrane 120, which may or may not include mechanical support layer 112.The purpose of acoustic absorption layer 118 is to absorb any acousticwaves that are not transferred into the CMOS substrate 140 and to avoidany acoustic waves transmitted in the “down” direction, so that theacoustic waves are reflected back to the membrane 120 and finallydetected. The acoustic absorption layer 118 may also be used as anadhesion or connection layer to fix the PMUT structure to a secondsubstrate, such as, e.g., a PCB (printed circuit board).

Although many of the operating principles of the inverted design and theoriginal non-inverted design are similar, there is an importantdifference in the generation and transmission of the acoustic waves. Inthe original design (e.g., FIGS. 1A-1B and 2), the acoustic waves aredirectly coupled into the acoustic coupling layer 114 due to thevibration of the membrane 120. In the inverted design herein, theacoustic waves are coupled into the CMOS substrate 140 through thevibration of the support structures such as e.g., edge support 102 andinterior support 104. As such, the support structures and membrane 120are designed to optimize the injection of the acoustic waves/energy intothe CMOS substrate 140. This means that the shape, size and placement ofthe support structures 102, 104 are optimized for the acousticinjection. For example, the interior support 104 may be wider than theedge support 102 in order to inject most acoustic energy at the interiorsupport and minimize acoustic injection at the edge supports. The shapeof the interior support 104 may, for example, be tapered by this reason.In some embodiments, where a uniform injection of the acoustic energy isrequired, all support structures 102, 104 may be of similar shape anddimension.

The ultrasonic transducer may be a PMUT device, such as described inconnection with FIGS. 1A and 1B, above. Alternatively, the ultrasonictransducer may be a bulk piezo actuator element, such as e.g., leadzirconate titanate (PZT).

FIG. 4 illustrates an embodiment of an ultrasonic transducer used in anelectronic device 450, such as an ultrasonic fingerprint sensing system.The electronic device, or fingerprint sensing system, 450 can include aplaten 416 onto which a human finger 452 may make contact. Ultrasonicsignals are generated and received by a plurality of ultrasonictransducers 400, such as an array of transducers 400, e.g., atwo-dimensional array. The platen 416 is formed on the first, or front,surface 440 a of the CMOS substrate 440. An acoustic coupling layer 414,such as a suitable epoxy, secures the platen, 416 to the first surface440 a of the CMOS substrate 440.

The ultrasonic transducer 400 is formed on the second, or back, surface440 b of the CMOS substrate 440 via wafer bonding or other suitabletechniques. The ultrasonic signals travel back and forth to theultrasonic transducer 400 through acoustic coupling layer 414, platen416, and CMOS substrate 440. Signal analysis is conducted using aprocessing logic module (e.g., including logic, control, andcommunication electronics) embedded in the CMOS substrate 440.Furthermore, any logic required to generate and/or detect the acousticwaves using ultrasonic transducer 400 may be embedded in the CMOSsubstrate. Any connections and/or vias required between the processinglogic and ultrasonic transducer may be adapted depending on the specificdesign and are not shown in the Figures. It will be appreciated that thesize of platen 416 and the other elements illustrated in FIG. 4 may bemuch larger (e.g., the size of a handprint) or much smaller (e.g., justa fingertip) than as shown in the illustration, depending on theparticular application. The ultrasonic transducer 400 includes themembrane 120 and exterior support structures 102, and, in someembodiments, the interior support structure 104, described above withreference to FIGS. 1A, 1B, 2, and 3. For clarity, these elements are notshown in FIG. 4.

In this example for fingerprinting applications, the human finger 452and the processing logic module in the CMOS substrate 440 can determine,based on a difference in interference of the acoustic signal withvalleys and/or ridges of the skin on the finger, an image depictingepidermis and/or dermis layers of the finger. Further, the processinglogic module can compare the image with a set of known fingerprintimages to facilitate identification and/or authentication. Moreover, inone example, if a match (or substantial match) is found, the identity ofuser can be verified. In another example, if a match (or substantialmatch) is found, a command/operation can be performed based on anauthorization rights assigned to the identified user. In yet anotherexample, the identified user can be granted access to a physicallocation and/or network/computer resources (e.g., documents, files,applications, etc.)

In another example, for finger-based applications, the movement of thefinger can be used for cursor tracking/movement applications. In suchembodiments, a pointer or cursor on a display screen can be moved inresponse to finger movement. It is noted that the processing logicmodule can include or be connected to one or more processors configuredto confer at least in part the functionality of the electronic device350. To that end, the one or more processors can execute codeinstructions stored in memory, for example, volatile memory and/ornonvolatile memory.

Also in accordance with the teachings herein, an image sensing systemincludes a CMOS substrate having a first surface and a second surfaceopposite the first surface and a sensor element comprising a pluralityof vibratory devices, such as ultrasonic transducers, a platen, and anacoustic coupling layer. The vibratory devices are formed on the secondsurface of the CMOS substrate, while the platen is formed over the firstsurface. The acoustic coupling layer couples the platen to the firstsurface. The CMOS substrate is between the plurality of ultrasonictransducers and the platen.

FIG. 5 illustrates in cross section one embodiment of an image sensingsystem 550 formed by connecting a plurality of ultrasonic devices 500 tothe second surface 540 b of a CMOS logic wafer 540, which includeslogic, control, and communication electronics. The ultrasonic devices500 have a transmit/receive surface 500 a attached to the second surface540 b. Thus, the ultrasonic devices 500 are configured to transmit andreceive ultrasonic signals through the second surface 540 b of the CMOSsubstrate 540. In an embodiment, a MEMS wafer including the plurality ofultrasonic devices 500 may be wafer-bonded to the second surface 540 b.In some embodiments, where the ultrasonic devices 500 are PMUT devices,each PMUT device 100 has a membrane 120 formed over a substrate 140 todefine a cavity 130, as described above in connection with FIG. 3, forexample. The membrane 120, primarily composed of silicon etched alongits periphery to form a relatively compliant section, is attached bothto a surrounding edge support 102. The membrane 120 is formed frommultiple layers, including a piezoelectric layer 110. The sensor may ormay not include an interior pinning support 104. In other embodimentsthe ultrasonic devices 500 are bulk piezo actuator elements, e.g., leadzirconate titanate (PZT).

The CMOS logic wafer 540 has a first, or front, surface 540 a and asecond, or back, surface 540 b opposite the first surface. Theultrasonic devices 500 are attached to the second surface 540 b. Theplaten 516 is attached to the first surface 540 a via an acousticcoupling material 514, such as a suitable epoxy. The ultrasonic devices500 may be embedded in an acoustic damping material 530, such as anepoxy. Connection to external circuitry, such as displays, may be madeby a flex connector 534 electrically attached to a contact 536. Invarious embodiments, acoustic waves emanate from the ultrasonic devices500, through the CMOS logic wafer 540 toward the platen 516.

Many variations may be made to enhance the signal strength or otherfeatures of the basic device shown in FIG. 3. For example, theelectrodes 106 and 108, the piezoelectric layer 110, and mechanicalsupport layer 112 (if present) may also be structured for maximumacoustic injection, for example, by creating maximum leverage of themembrane 120 onto the interior support structure 104. In one embodiment,as shown in FIG. 6, the first electrodes 106 may be positioned closer tothe interior support structure 104 for increased signal strength.Alternatively, depending on the desired mode of operation, the firstelectrodes 106 may be placed closer to edge support structures 102.Piezoelectric layer 110 may be continuous, or may also be structured, asshown in FIG. 7. in order to control the propagation of piezoelectricstress for maximum leverage.

FIG. 7 is similar to FIG. 6, and FIG. 7 illustrates maximizingdisplacement of the support structures, here, the interior supportstructure 104, by altering the membrane 120, such as by creatingopenings or voids 110 a in parts of the piezoelectric layer 110, orother parts of membrane 120, to provide a non-uniform but continuouslayer. As an alternative to voids, local thickness variations may beused. In this connection, displacement of the piezoelectric layer 110may be optimized by having the layer thinner in the middle portion andthicker at the edge portion. One or more layers of the membrane may bealtered, for example by creating voids or local variations of thickness,with the goal of optimizing the efficiency of the transducer such as bymaximizing the displacements of any of the structures used to generatethe acoustic energy/waves.

In some embodiments, the membrane-and-cavity design may be replaced by asimpler piezoelectric elements design as shown in FIG. 8. In theseembodiments, the piezoelectric layer 110 comprises a layer of bulkpiezoelectric material such as, but not limited to, aluminum nitride(AlN), lead zirconate titanate (PZT), scandium doped aluminum nitride(ScAlN), quartz, polyvinylidene fluoride (PVDF), and/or zinc oxide, andis positioned between the first electrode 106 and the second electrode108, with the second electrode 108 in contact with the substrate 140. Anoptional mechanical support layer and acoustic absorption layer 118 maybe used. The shape of the piezoelectric layer 110 may also be adaptedfor maximum acoustic injection, for example, as indicated in FIG. 9,which is otherwise similar to FIG. 8.

In some embodiments, an array of support structures 105 may be depositedbetween the substrate 140 and the membrane 120, such as shown in FIG.10. The first electrodes 106 may be structured to address thepiezoelectric material associated with the different support structures104, 105. The structure depicted in FIG. 10 may be considered to ahybrid bulk piezo and PMUT structure, where the piezoelectric layer 110is associated with electrodes 106, 108 and the support structures 104,105 support the CMOS layer 140. The first electrode 106 is beneath thesupport structure 104, 105 instead of next to it.

The objective is to inject the acoustic waves/energy at the locations ofthe different support structures 104, 105. The various electrodes 106,108 and support structures 104, 105 may not only work individually, butin some embodiments an array of structures may work together. Forexample, some structures may function as transmission structure 104 thatgenerate the acoustic waves and some structures may function as drivestructures 105, and the drive structures 105 may be operated to create amaximum of acoustic energy of the acoustic waves at transmissionstructures 104. One or both of the transmission structures 104 and drivestructures 105 may be used to detected the reflected acousticwaves/energy.

The drive structures and transmission structures may have an exemplary2D layout as indicated in FIG. 11, where a single transmission structureis surrounded by an array, here, hexagonal, of drive structures. Morecomplicated patterns using a plurality of rings of drive structuresaround the transmission structure may be used, and the phase differenceof the driving signals of the different structures may be optimized formaximum acoustic injection. By shifting the drive-transmission pattern,other structures may be used as transmission structures, as indicated byarrow A in FIG. 11. The drive structure pins 105 move in a way tomaximize displacement of the transmission structure pins 104.

A method 1200 for ultrasonic sensing using an electronic device 450 isillustrated in FIG. 12. In the method 1200, a CMOS substrate 440 havinga first surface 440 a and a second surface 440 b opposite the firstsurface is provided 1205. A plurality of ultrasonic transducers 400having a transmit/receive surface 400 a is formed 1210 on the secondsurface 440 b of the CMOS substrate 440. The transmit/receive surface400 a is disposed on the second surface 440 b. A platen 416 is formed1215 on the first surface 440 a and has a contact surfacepiezoelectrically associated with the plurality of ultrasonictransducers 400. In this manner, the CMOS substrate 440 is sandwichedbetween the plurality of ultrasonic transducers 400 and the platen 416.

An acoustic coupling layer 414 may be formed on the first surface 440 ato which the platen 416 is secured. The acoustic coupling layer 414 maybe a suitable epoxy, for example.

The electronic device 450 is configured to sense a fingerprint of ahuman finger 452. The sensing element may be configured to sense a palmprint, a fingertip, or other suitable object.

The plurality of ultrasonic transducers 400 may be at least partlyencapsulated in an acoustic damping epoxy (shown as acoustic dampingepoxy 530 in FIG. 5).

In the method 1200 for ultrasonic (or image) sensing, acoustic waves maybe emitted towards the platen 416 through the CMOS substrate 440. Theacoustic waves that reflect off an object 452 on the platen 416 may thenbe detected and processed by the logic, control, and communicationelectronics in the CMOS substrate 440.

Example Mobile Electronic Device

Turning now to the figures, FIG. 13 is a block diagram of an examplemobile electronic device 1300 upon which embodiments described hereinmay be implemented. As will be appreciated, mobile electronic device1300 may be implemented as a device or apparatus, such as a handheldmobile electronic device. For example, such a mobile electronic devicemay be, without limitation, a mobile telephone phone (e.g., smartphone,cellular phone, a cordless phone running on a local network, or anyother cordless telephone handset), a wired telephone (e.g., a phoneattached by a wire), a personal digital assistant (PDA), a video gameplayer, video game controller, a navigation device, an activity orfitness tracker device (e.g., bracelet, clip, band, or pendant), a smartwatch or other wearable device, a mobile internet device (MID), apersonal navigation device (PND), a digital still camera, a digitalvideo camera, a portable music player, a portable video player, aportable multi-media player, a remote control, or a combination of oneor more of these devices.

As depicted in FIG. 13, mobile electronic device 1300 may include a hostprocessor 1310, a host bus 1320, a host memory 1330, a display device1340, and a sensor processing unit 1370. Some embodiments of mobileelectronic device 1300 may further include one or more of an interface1350, a transceiver 1360 (all depicted in dashed lines) and/or othercomponents. In various embodiments, electrical power for mobileelectronic device 1300 is provided by a mobile power source such as abattery (not shown), when not being actively charged.

Host processor 1310 can be one or more microprocessors, centralprocessing units (CPUs), DSPs, general purpose microprocessors, ASICs,ASIPs, FPGAs or other processors which run software programs orapplications, which may be stored in host memory 1330, associated withthe functions and capabilities of mobile electronic device 1300.

Host bus 1320 may be any suitable bus or interface to include, withoutlimitation, a peripheral component interconnect express (PCIe) bus, auniversal serial bus (USB), a universal asynchronousreceiver/transmitter (UART) serial bus, a suitable advancedmicrocontroller bus architecture (AMBA) interface, an Inter-IntegratedCircuit (I2C) bus, a serial digital input output (SDIO) bus, a serialperipheral interface (SPI) or other equivalent. In the embodiment shown,host processor 1310, host memory 1330, display 1340, interface 1350,transceiver 1360, sensor processing unit (SPU) 1370, and othercomponents of mobile electronic device 1300 may be coupledcommunicatively through host bus 1320 in order to exchange commands anddata. Depending on the architecture, different bus configurations may beemployed as desired. For example, additional buses may be used to couplethe various components of mobile electronic device 1300, such as byusing a dedicated bus between host processor 1310 and memory 1330.

Host memory 1330 can be any suitable type of memory, including but notlimited to electronic memory (e.g., read only memory (ROM), randomaccess memory, or other electronic memory), hard disk, optical disk, orsome combination thereof. Multiple layers of software can be stored inhost memory 1330 for use with/operation upon host processor 1310. Forexample, an operating system layer can be provided for mobile electronicdevice 1300 to control and manage system resources in real time, enablefunctions of application software and other layers, and interfaceapplication programs with other software and functions of mobileelectronic device 1300. Similarly, a user experience system layer mayoperate upon or be facilitated by the operating system. The userexperience system may comprise one or more software application programssuch as menu navigation software, games, device function control,gesture recognition, image processing or adjusting, voice recognition,navigation software, communications software (such as telephony orwireless local area network (WLAN) software), and/or any of a widevariety of other software and functional interfaces for interaction withthe user can be provided. In some embodiments, multiple differentapplications can be provided on a single mobile electronic device 1300,and in some of those embodiments, multiple applications can runsimultaneously as part of the user experience system. In someembodiments, the user experience system, operating system, and/or thehost processor 1310 may operate in a low-power mode (e.g., a sleep mode)where very few instructions are processed. Such a low-power mode mayutilize only a small fraction of the processing power of a full-powermode (e.g., an awake mode) of the host processor 1310.

Display 1340, may be a liquid crystal device, (organic) light emittingdiode device, or other display device suitable for creating and visiblydepicting graphic images and/or alphanumeric characters recognizable toa user. Display 1340 may be configured to output images viewable by theuser and may additionally or alternatively function as a viewfinder forcamera.

Interface 1350, when included, can be any of a variety of differentdevices providing input and/or output to a user, such as audio speakers,touch screen, real or virtual buttons, joystick, slider, knob, printer,scanner, computer network I/O device, other connected peripherals andthe like.

Transceiver 1360, when included, may be one or more of a wired orwireless transceiver which facilitates receipt of data at mobileelectronic device 1300 from an external transmission source andtransmission of data from mobile electronic device 1300 to an externalrecipient. By way of example, and not of limitation, in variousembodiments, transceiver 1360 comprises one or more of: a cellulartransceiver, a wireless local area network transceiver (e.g., atransceiver compliant with one or more Institute of Electrical andElectronics Engineers (IEEE) 802.11 specifications for wireless localarea network communication), a wireless personal area networktransceiver (e.g., a transceiver compliant with one or more IEEE 802.15specifications for wireless personal area network communication), and awired a serial transceiver (e.g., a universal serial bus for wiredcommunication).

Mobile electronic device 1300 also includes a general purpose sensorassembly in the form of integrated SPU 1370 which includes sensorprocessor 1372, memory 1376, an ultrasonic sensor 1378 (e.g., imagesensing system 550), and a bus 1374 for facilitating communicationbetween these and other components of SPU 1370. In some embodiments, SPU1370 may include at least one sensor 1380 (shown as sensor 1380-1,1380-2, . . . 1380-n) communicatively coupled to bus 1374. In someembodiments, all of the components illustrated in SPU 1370 may beembodied on a single integrated circuit. It should be appreciated thatSPU 1370 may be manufactured as a stand-alone unit (e.g., an integratedcircuit), that may exist separately from a larger electronic device.

Sensor processor 1372 can be one or more microprocessors, CPUs, DSPs,general purpose microprocessors, ASICs, ASIPs, FPGAs or other processorswhich run software programs, which may be stored in memory 1376,associated with the functions of SPU 1370.

Bus 1374 may be any suitable bus or interface to include, withoutlimitation, a peripheral component interconnect express (PCIe) bus, auniversal serial bus (USB), a universal asynchronousreceiver/transmitter (UART) serial bus, a suitable advancedmicrocontroller bus architecture (AMBA) interface, an Inter-IntegratedCircuit (I2C) bus, a serial digital input output (SDIO) bus, a serialperipheral interface (SPI) or other equivalent. Depending on thearchitecture, different bus configurations may be employed as desired.In the embodiment shown, sensor processor 1372, memory 1376, sensor1378, and other components of SPU 1370 may be communicatively coupledthrough bus 1374 in order to exchange data.

Memory 1376 can be any suitable type of memory, including but notlimited to electronic memory (e.g., read only memory (ROM), randomaccess memory, or other electronic memory). Memory 1376 may storealgorithms or routines or other instructions for processing datareceived from ultrasonic sensor 1378 and/or one or more sensor 1380, aswell as the received data either in its raw form or after someprocessing. Such algorithms and routines may be implemented by sensorprocessor 1372 and/or by logic or processing capabilities included inultrasonic sensor 1378 and/or sensor 1380.

A sensor 1380 may comprise, without limitation: a temperature sensor, ahumidity sensor, an atmospheric pressure sensor, an infrared sensor, aradio frequency sensor, a navigation satellite system sensor (such as aglobal positioning system receiver), an acoustic sensor (e.g., amicrophone), an inertial or motion sensor (e.g., a gyroscope,accelerometer, or magnetometer) for measuring the orientation or motionof the sensor in space, or other type of sensor for measuring otherphysical or environmental quantities. In one example, sensor 1380-1 maycomprise an acoustic sensor, sensor 1380-2 may comprise a secondacoustic sensor, and sensor 1380-n may comprise a motion sensor.

In some embodiments, ultrasonic sensor 1378 and/or one or more sensors1380 may be implemented using a microelectromechanical system (MEMS)that is integrated with sensor processor 1372 and one or more othercomponents of SPU 1370 in a single chip or package. Although depicted asbeing included within SPU 1370, one, some, or all of ultrasonic sensor1378 and/or one or more sensors 1380 may be disposed externally to SPU1370 in various embodiments. It should be appreciated that image sensingsystem 550 of FIG. 5 is an example of ultrasonic sensor 1378.

What has been described above includes examples of the subjectdisclosure. It is, of course, not possible to describe every conceivablecombination of components or methodologies for purposes of describingthe subject matter, but it is to be appreciated that many furthercombinations and permutations of the subject disclosure are possible.Accordingly, the claimed subject matter is intended to embrace all suchalterations, modifications, and variations that fall within the spiritand scope of the appended claims.

In particular and in regard to the various functions performed by theabove described components, devices, circuits, systems and the like, theterms (including a reference to a “means”) used to describe suchcomponents are intended to correspond, unless otherwise indicated, toany component which performs the specified function of the describedcomponent (e.g., a functional equivalent), even though not structurallyequivalent to the disclosed structure, which performs the function inthe herein illustrated exemplary aspects of the claimed subject matter.

The aforementioned systems and components have been described withrespect to interaction between several components. It can be appreciatedthat such systems and components can include those components orspecified sub-components, some of the specified components orsub-components, and/or additional components, and according to variouspermutations and combinations of the foregoing. Sub-components can alsobe implemented as components communicatively coupled to other componentsrather than included within parent components (hierarchical).Additionally, it should be noted that one or more components may becombined into a single component providing aggregate functionality ordivided into several separate sub-components. Any components describedherein may also interact with one or more other components notspecifically described herein.

In addition, while a particular feature of the subject innovation mayhave been disclosed with respect to only one of several implementations,such feature may be combined with one or more other features of theother implementations as may be desired and advantageous for any givenor particular application. Furthermore, to the extent that the terms“includes,” “including,” “has,” “contains,” variants thereof, and othersimilar words are used in either the detailed description or the claims,these terms are intended to be inclusive in a manner similar to the term“comprising” as an open transition word without precluding anyadditional or other elements.

Thus, the embodiments and examples set forth herein were presented inorder to best explain various selected embodiments of the presentinvention and its particular application and to thereby enable thoseskilled in the art to make and use embodiments of the invention.However, those skilled in the art will recognize that the foregoingdescription and examples have been presented for the purposes ofillustration and example only. The description as set forth is notintended to be exhaustive or to limit the embodiments of the inventionto the precise form disclosed.

What is claimed is:
 1. An electronic device comprising: a CMOS substratehaving a first surface and a second surface opposite the first surface;a two-dimensional array of Piezoelectric Micromachined UltrasonicTransducer (PMUT) devices, wherein each PMUT device is independentlyoperable to generate and receive ultrasonic signals, and wherein thetwo-dimensional array of PMUT devices is disposed on the second surfaceof the CMOS substrate, wherein at least one PMUT device comprises: anedge support structure connected to the CMOS substrate; and a membraneconnected to the edge support structure such that a cavity is definedbetween the membrane and the CMOS substrate, the membrane configured toallow movement at ultrasonic frequencies, the membrane comprising: apiezoelectric layer; first and second electrodes coupled to opposingsides of the piezoelectric layer; and a mechanical support layer; and acontact surface piezoelectrically associated with the two-dimensionalarray of PMUT devices and disposed on the first surface; wherein theCMOS substrate is between the two-dimensional array of PMUT devices andthe contact surface such that the ultrasonic signals are emitted fromthe two-dimensional array of PMUT devices through the CMOS substratetoward the contact surface and reflected ultrasonic signals travelthrough the CMOS substrate for receipt at the two-dimensional array ofPMUT devices.
 2. The electronic device of claim 1, wherein the at leastone PMUT device further comprises an interior support structure disposedwithin the cavity and connected to the CMOS substrate and the membrane.3. The electronic device of claim 2, wherein at least one of the edgesupport structure and the interior support structure is configured in atleast one of shape, size and placement to optimize acoustic injectioninto the CMOS substrate.
 4. The electronic device of claim 1, whereinthe contact surface is a platen.
 5. The electronic device of claim 1,further including an epoxy disposed on the second surface of the CMOSsubstrate and encapsulating the two-dimensional array of PMUT devices.6. The electronic device of claim 5, wherein the epoxy is acousticallydamping.
 7. The electronic device of claim 1 wherein the contactsurface, the CMOS substrate, and the two-dimensional array of PMUTdevices are configured to operate as a sensor.
 8. The electronic deviceof claim 7, wherein the contact surface is adapted to receive a humanfinger for sensing a fingerprint.
 9. The electronic device of claim 1,wherein the contact surface is acoustically coupled to the first surfaceof the CMOS substrate.
 10. The electronic device of claim 1, wherein theCMOS substrate comprises logic, control, and communication electronics,to which the two-dimensional array of PMUT devices is connected.
 11. Amobile electronic device comprising: a host processor; a host memory;and an ultrasonic sensor comprising: a CMOS substrate having a firstsurface and a second surface opposite the first surface, the CMOSsubstrate comprising logic, control, and communication electronics; aplurality of Piezoelectric Micromachined Ultrasonic Transducer (PMUT)devices formed on the second surface of the CMOS substrate, each PMUTdevice independently operable to emit and receive acoustic waves,wherein at least one PMUT device comprises: an edge support structureconnected to the CMOS substrate; and a membrane connected to the edgesupport structure such that a cavity is defined between the membrane andthe CMOS substrate, the membrane configured to allow movement atultrasonic frequencies, the membrane comprising: a piezoelectric layer;first and second electrodes coupled to opposing sides of thepiezoelectric layer; and a mechanical support layer connected to thefirst electrode; and a platen formed over the first surface; wherein theCMOS substrate is between the plurality of PMUT devices and the platensuch that the acoustic waves are emitted from the plurality of PMUTdevices through the CMOS substrate toward the platen and reflectedacoustic waves travel through the CMOS substrate for receipt at theplurality of PMUT devices.
 12. The mobile electronic device of claim 11,wherein the PMUT device further comprises an interior support structuredisposed within the cavity and connected to the CMOS substrate and themembrane.
 13. The mobile electronic device of claim 11, wherein theplaten comprises a contact surface adapted to receive a human finger forsensing a fingerprint.
 14. The mobile electronic device of claim 11,wherein the ultrasonic sensor is configured to sense a fingerprint of ahuman finger.
 15. A method for ultrasonic sensing using an electronicdevice, the method comprising: providing a CMOS substrate having a firstsurface and a second surface opposite the first surface; forming atwo-dimensional array of Piezoelectric Micromachined UltrasonicTransducer (PMUT) devices, wherein each PMUT device is independentlyoperable to generate and receive ultrasonic signals, and wherein thetwo-dimensional array of PMUT devices is disposed on the second surfaceof the CMOS substrate, wherein at least one PMUT device comprises: anedge support structure connected to the CMOS substrate; and a membraneconnected to the edge support structure such that a cavity is definedbetween the membrane and the CMOS substrate, the membrane configured toallow movement at ultrasonic frequencies, the membrane comprising: apiezoelectric layer; first and second electrodes coupled to opposingsides of the piezoelectric layer; and a mechanical support layer; andforming a platen on the first surface and having a contact surfacepiezoelectrically associated with the two-dimensional array of PMUTdevices, wherein the CMOS substrate is between the two-dimensional arrayof PMUT devices and the platen such that the ultrasonic signals areemitted from the two-dimensional array of PMUT devices through the CMOSsubstrate toward the contact surface and reflected ultrasonic signalstravel through the CMOS substrate for receipt at the two-dimensionalarray of PMUT devices.